1. Field of the Invention
This invention relates generally to power woodworking, machine and other bench tools for cutting, shaping and drilling a workpiece and more specifically to apparatus for stabilizing the workpiece during its displacement relative to the tool.
2. Description of Related Art
Power woodworking and machine tools to which this invention pertains include table saws, radial arm saws, shapers, router tables, drill presses and the like. These tools, hereinafter call "bench tools," comprise certain basic components. Each has a "work surface" that supports the workpiece. Tables associated with each of the specified bench tools and others typically provide such a work surface. Bench tools also include a cutting mechanism, or cutting tool, such as a saw blade, drill bit, router bit or the like, and an arbor or chuck for attaching the cutting tool to an electric motor.
A typical table provides a horizontal work surface that supports the workpiece during its relative displacement with respect to the cutting tool. On some bench tools, the operator moves the workpiece across the work surface into contact with a cutting tool that is at a fixed position on the table. For example, a table saw comprises a motorized circular saw supported below a horizontal work surface. The top portion of the saw blade extends above the work surface into the tool work plane where cutting takes place. The operator slides a workpiece along the work surface past the rotating blade thereby to cut the workpiece. On other bench tools, the workpiece is stationary on the work surface while the cutting tool is moved into contact with the workpiece. For example, in a drill press a vertically oriented drill displaces along a vertical axis into a workpiece held in one position on the work surface. A radial arm saw is another example of such a bench tool.
Some bench tools, such as table saws, router tables and shapers, often include a vertical fence that mounts to the table adjacent to the cutting tool. Prior art fences generally comprise one or more square or rectangular plates mounted on the bench work surface perpendicular to the work surface. As an operator moves the workpiece past the cutting tool, the fence engages a vertical workpiece surface to stabilize the horizontal position of the workpiece relative to the cutting unit. The fence thus establishes a "second work surface" that is substantially perpendicular to the plane of the horizontal work surface that the table defines.
In order to move a workpiece in a straight line, an operator must exert a force on the workpiece that has three orthogonally directed components. A first or vertical component is perpendicular to the work surface to maintain firm contact between the workpiece and the horizontal work surface. A second or horizontal component is parallel to the work surface and normal to the fence to maintain the workpiece against the fence. The third is another horizontal component parallel to the fence to displace the workpiece past the cutting tool. On a table saw, for example, the operator must continuously hold the workpiece horizontally against the fence and vertically on the work surface while simultaneously feeding the workpiece toward and past the cutting saw blade.
It is often difficult to maintain such orthogonal forces uniformly against the workpiece as it moves. This is particularly true with woodworking tools because the wood is not uniform, so the resistance to pressure produced as the workpiece engages the cutting tool can vary greatly and unexpectedly. It can also be particularly difficult to simultaneously push a long workpiece toward the cutting blade while holding the workpiece firmly against the fence, since the operator must initially push the back end of the workpiece, which may be a substantial distance from the tool and fence, toward the cutting tool. If the workpiece moves relative to the fence, an uneven cut results. If the workpiece moves relative to the horizontal work surface, the cutting tool can drive the workpiece back toward the operator. Finally, it becomes difficult and dangerous to maintain all these force components as the end of a workpiece passes the cutting tool because the operator's fingers often are proximate the cutting tool.
U.S. Pat. No. 552,610 to Fisher discloses a protective hood that extends over a cutting blade on a jointer or shaper to prevent an operator's hands from contacting the cutting blade. The hood moves vertically relative to a fence according to the size of wood being cut. The hood also reciprocates horizontally with respect to the fence to cover the cutting blade during use.
U.S. Pat. No. 2,895,517 to Rhett discloses a protective guard for a jointer that closes behind the back end of a workpiece and toward a fence to prevent an operator's fingers from contacting the cutting blade. The guard is spring-projected toward the fence and comprises a leading member with a cam edge and a trailing frame member that supports a plurality of posts, each of which is independently spring-projected toward the fence. As the leading end of a workpiece engages the cam edge of the leading member, the guard moves from the fence to allow for continued feeding of the workpiece. As the trailing end passes the leading member, a spring drives the leading member back to the fence before the operator's fingers can reach the cutting tool. Simultaneously, the posts move into abutting engagement with the workpiece thereby to cover the cutterhead while the workpiece passes over the cutterhead. As the trailing end of the workpiece moves past the cutterhead, the posts are driven sequentially toward the fence
U.S. Pat. No. 1,394,499 to Ingstrum discloses a protective guard for a jointer that comprises an elongated extendable body with a pivoted, spring-biased toggle arm at one end. The guard covers a rotating hub whenever a table is not being used. As a workpiece advances along a fence toward the cutterhead, it engages a cam head and pivots the toggle arm toward the fence to move the protective guard away from the fence. This allows the workpiece to pass the elongated body. When the trailing end of the workpiece passes the toggle arm, the toggle arm pivots away from the fence, and the elongated body returns to its extended position against the fence.
The apparatus disclosed in each of the foregoing patents forces a workpiece against a fence as the workpiece passes a cutting tool. However, the apparatus applies such lateral pressure only at the point where the workpiece engages the cutting tool. The apparatus does not apply uniform pressure along the entire length of the workpiece or along any continuous substantial portion thereof. The operator's ability to push the workpiece in a straight path past the cutting tool in contact with a fence and work surface is still required. Moreover, the apparatus is adapted for use with a single type bench tool. Fisher discusses jointers or shapers; Rhett and Ingstrum only discuss jointers. The structures are not readily adapted for use with a wide variety of bench tools including, but not limited to, table saws, radial arm saws, router tables, shapers and drill presses.